This invention relates to hydraulic control apparatus in general and more specifically to a hydraulic control apparatus comprising a hydraulic master cylinder and a hydraulic slave cylinder for operating a mechanism remotely located from the master cylinder such for example as the clutch of a motor vehicle.
It is known to prefill with hydraulic fluid a motor vehicle clutch control apparatus comprising a master cylinder, a reservoir of hydraulic fluid, and a slave cylinder for operating the throw-out bearing of a mechanical diaphragm spring clutch, as disclosed in British patent number 1,539,879 and in corresponding U.S. Pat. Nos. 4,407,125 and 4,599,860 assigned to the assignee of the present invention. In addition, U.S. Pat. Nos. 4,503,678, 4,516,507, 4,585,106, 4,585,107, 4,585,108 and 4,585,109, all assigned to the assignee of the present invention, also disclose diverse forms of prefilled hydraulic control apparatus for motor vehicle clutches.
Prefilling with hydraulic fluid and pretesting hydraulic apparatus for operating motor vehicle mechanisms such as mechanical clutches present the many advantages for the motor vehicle manufacturer of receiving a fully assembled mechanism comprising all of the components filled with hydraulic fluid and pretested for proper operation ready to install on a motor vehicle on the assembly line without requiring that the components be installed, separately connected by way of a rigid or flexible conduits, and filled after installation with hydraulic fluid while being purged of any atmospheric air contained in the apparatus.
To simplify the installation of a hydraulic control apparatus in a motor vehicle, and particularly in situations where the apparatus employs a concentric slave cylinder as the clutch actuating device, it is known to provide the control apparatus with a one way quick connect coupling or connector either at some point along the flexible conduit connecting the master cylinder to the slave cylinder or at the end of the conduit connected to the master cylinder or at the end of the conduit connected to the slave cylinder. The one-way quick connect coupling is arranged such that after the hydraulic control apparatus has been assembled, prefilled with hydraulic fluid, and pretested, the connection between the master cylinder and slave cylinder may be broken without loss of fluid, or negligible loss of fluid. The apparatus may thus be shipped to the motor vehicle manufacturer completely filled with hydraulic fluid but in two separate modules such that the concentric slave cylinder may be made a part of the clutch bell housing, or of the transmission casing. This allows the slave cylinder clutch bell housing assembly, or the slave cylinder transmission casing assembly, to be installed in the motor vehicle at whatever station on the assembly line that the clutch or transmission is installed and the master cylinder may be installed in the motor vehicle also at whatever appropriate station and the two cylinders connected together without any loss or negligible loss of fluid and without introduction of air into the apparatus. Whereas module systems of this type have proven to be generally satisfactory, there is still a need to provide a bleed system in the apparatus to facilitate initial filling of the apparatus and/or to facilitate field maintenance and, specifically, field maintenance where it is necessary to bleed the system and refill the system. Whereas the prior art control apparatus have typically included a bleed system in the apparatus, for example in association with the slave cylinder, the prior art bleed systems have complicated the structure of the apparatus and have added to the cost of the apparatus.